The present invention relates to an electronically scanned antenna working in a wide frequency band. It can be used especially in applications requiring compact or a low-cost antennas.
An electronically scanned antenna comprises a network of microwave sources associated with a phase-shifter. It is known that the direction of the antenna beam depends on the phase shifts applied by the phase-shifters to the source signals. For a given state of the phase-shifters and a given frequency, a well-defined direction of antenna beam is obtained. However, for this same state of the phase-shifters, when the sending frequency varies, there is a deflection of the antenna beam. There are many applications that require the instantaneous sending of a frequency band of varying width. This is the case especially with SAR (Synthetic Aperture Radar) type radar imaging applications. Such applications work, for example, in instantaneous bands in the range of several hundreds of MHz or even more. The use of standard electronically scanned antennas prompts a dispersal of antenna aiming with respect to frequency variations as in a sprinkling or scattering process, thus preventing especially the obtaining of precise images.
These deflections due to the frequency variations cannot be compensated for in the control of the phase-shifters because their maximum phase shift is limited to 360°. A known approach to compensating for these deflections consists then in using true delay lines. However, such an approach particularly complicates the structure of the antennas: it increases their weight and also their cost.